I am trying to learn Esperanto, and really needed a break from the lessons. So I thought I'd try my hand and forming some sentences on my own. I am sure I butchered it pretty well, but could someone point out what I did wrong, and what I should have done?

My attempt:

Kato en botojn

Iam estis, muelisto kiu havis tri filojn. La muelisto estis tre maljuna, kaj decidis apartigi liajn tutajn posedajxoj inter liaj tri filoj. La unua filo, kun cerboeg kaj koroeto, ricevis la muelejon. Li posedis bonan komprenon pri komerco. La dua filo, kun cerbeto kaj spinego, ricevis la mulon. Li diligentegis. La tria filo, kun cerbeto kaj koroego, ricevis la katon.

What I was trying to say:
Puss in boots

Once upon a time, a miller had three sons. The miller was very old, and decided to divide his possessions between his three sons. The first son, with a large brain, and small heart, received the mill. He had good business sense. The second son, with a small brain and large back, received the mule. He was a very hard worker. The third son, with a small brain, and a big heart, received the cat.

I think I am jumping the gun a bit trying this, but I couldn't take one more "See Jane. See Jane run. Run Jane run." lesson without trying something fun-ish.

Grubbycup:
Kato en botojn

Iam estis muelisto, kiu havis tri filojn. La muelisto estis tre maljuna, kaj decidis apartigi liajn tutajn posedaĵojn inter liaj tri filoj. La unua filo, kun mensego kaj koreto, ricevis la muelejon. Li posedis bonan komprenon pri komerco. La dua filo, kun menseto kaj spinego, ricevis la mulon. Li diligentegis. La tria filo, kun menseto kaj korego, ricevis la katon.

My edits in bold. Remember that numbers don't take the accusative, and suffixes are placed before part-of-speech endings (koreto, not koroet).

Thank you very much for your help and time. I think I understand all the edits except for the changing of cerbo with menso. As I understand it, menso is mind, where cerbo is the brain. Since I used the organ names for heart and spine, why make the change? I am not arguing, I'm just trying to understand. I really appreciate your help, since I am stumbling around with my learning and trying to get a grasp on things.

EDIT: Ok, so nevermind (pun intended), I am guessing that you did it because that's how I wrote it in my translation. My spaz.

Grubbycup: As I understand it, menso is mind, where cerbo is the brain. Since I used the organ names for heart and spine, why make the change?...

I think you're right, though I'm quite sure that Oŝo-Jabe was trying to be helpful as possible.

But also, I would use granda for 'big' and malgranda (or possibly eta) for 'small'.

Thus I would put it La unua filo, kun granda cerbo kaj malgranda koro, etc.